The invention relates to a lancing system for withdrawing a body fluid from the skin of a human or animal. The body fluid is typically blood. Many applications, however, are concerned with acquiring a sample of interstitial liquid. Hereafter reference is made, without restriction of the generality, to blood as an example, also for other body fluids which can be acquired from the skin.
The system includes a lancing element adapted for single use (disposable) for piercing into the skin, and a lancing instrument having a drive for driving the lancing movement.
Disposable lancing elements are used since many years for withdrawing a small quantity of blood from a body part (usually from a finger or ear lobe) for analytic-diagnostic purposes. In this context, the lancing elements are typically referred to as lancets. Lancets provided for manual piercing are typically used by medically trained personnel. Nevertheless the piercing causes significant pain.
Lancing instruments which contain a lancing drive are also used since many years. The lancing instrument can be implemented as disposable item having a fixedly integrated lancet. More common are instruments which are usable multiple times and have a coupling element, by which one lancet at a time can be replaceably connected to the lancing drive. The instruments and lancets are elements which are adapted to one another and are provided by the same producer. They are therefore designated as a “lancing system” or “blood withdrawal system”.
A spring is typically used as the drive source for the lancing drive in the housing of the lancing instrument. However, other drive sources are also used, such as an electric motor or an electromagnetic linear drive. A lancing element guide is provided to ensure that the lancing movement takes place on a predetermined lancing path.
At the beginning of the development, very simple designs of the drive were typical, in which the lancet was fastened directly to one end of a compression spring positioned in an elongated housing (U.S. Pat. No. 4,469,110). In order to control the lancing depth, in such systems, the movement path of the lancet in the lancing direction was limited by a stop surface of the lancet hitting a corresponding lancing depth limiting stop in the housing of the lancing instrument.
In another design, described in U.S. Pat. No. 4,442,836, the movement of the lancet is driven by a first spring in the direction toward the skin surface up to a reversal point (forward phase of the lancing movement), while a second spring is used as the drive source for the retraction movement of the lancet (retraction phase of the lancing movement). The second spring becomes effective after a force coupling between the first spring and the lancet has been interrupted. In order to ensure a defined position of the reversal point of the lancet movement, the force transmission between the drive spring and the lancet is interrupted at a defined point of the movement path.
Blood withdrawal systems of this type do not meet the high requirements which are to be fulfilled if regular monitoring of specific analytic values of the blood is required. This applies in particular for diabetics, who must monitor their blood sugar frequently, in order to keep their blood sugar level continuously within specific target limits, by insulin injections which are adapted to the demand (which varies strongly as a function of the food consumption, physical activity, etc.). It has been proven by extensive scientific studies that a dramatic regression of the most severe long-term damages of diabetes mellitus (for example, retinopathy with resulting blinding of the patient) can be achieved using intensive therapy on the basis of at least four blood analyses per day.
Great progress in this regard has been achieved by a drive type which can be designated as the “housing-coupled drive”. Such a drive comprises a transmission, by which a movement of the drive source (such as a spring or electric motor) is converted into a lancing movement of the lancing element, the transmission including a housing coupling mechanism, which comprises at least two transmission links, a housing bearing, and a coupling element for coupling the lancing element thereto. A first housing-side transmission link is connected to the housing of the lancing instrument by means of the housing bearing, and a second lancing-element-side transmission link is connected to the coupling element. The lancing element is connected via the housing coupling mechanism to a part of the housing of the lancing instrument in such a manner that it is moved axially in the direction of the lancing movement and is connected to the housing part and that a specified distance from the housing part is ensured at the reversal point of the lancing movement. Housing-coupled drives are known in various embodiments:                U.S. Pat. No. 4,924,879 discloses a lancing instrument having a rotor which is borne by the housing and driven by a spring, and which is coupled via a connecting rod to the lancing element. The rotor forms the housing-side transmission link and the housing bearing forms its rotational bearing. The lancing-element-side transmission link is formed by the connecting rod, to which a lancing element holder is coupled via a pivot joint, the holder acting as a coupling element for coupling the lancing element thereto.        U.S. Pat. No. 5,318,584 also discloses a lancet drive having a drive rotor on which a drive spring acts on one side (drive side) and which is coupled on the other side via a control curve to the lancet so that the rotation of the drive rotor is converted into the desired lancing movement. In this case, the rotor again forms the housing-side transmission link and the housing bearing forms its rotational bearing. The lancing-element-side transmission link is formed by a control curve rider, which travels along its control curve during the rotation of the drive rotor and is fixedly connected to a lancet holder, which forms the coupling element for coupling the lancet thereto.        Further embodiments of housing-coupled drives having rotors are described in U.S. Pat. No. 7,223,276. The housing-side transmission link is again formed by a drive rotor having a control curve and the lancing-element-side transmission link is formed by a control curve rider, which is fixedly connected to a coupling element for coupling a lancing element thereto. Deviating from the above-mentioned embodiments, the coupling element is in this case not a lancing element holder, in which the lancing element is seated and which is guided in the housing by an axial guide and thus indirectly guides the lancing element. Rather, the lancing element is directly guided in a corresponding hole of the lancing instrument. At its rear end it has a recess which allows the coupling element (in this case a coupling rod head) to be coupled on.        U.S. Pat. No. 6,858,015 describes a design in which the coupling element is connected to the lancing instrument housing by means of levers which are coupled via pivot joints. The coupling element is formed by a lancet holder, which is connected via a pivot joint to a housing-side pivot lever, which forms the lancing-element-side transmission link. The housing-side transmission link is formed by a second pivot lever, which is linked via a further pivot bearing to the housing. The housing bearing is in this case not immovably fastened on the housing, but rather arranged and adapted in such a manner that it is displaceable in the tensioning phase of the lancet drive. However, the design makes sure that the housing bearing is located in a precisely defined position relative to the housing when the lancing movement is executed, in particular when the lancing element is located at the reversal point of the lancing movement. This is decisive for the precision of the lancing depth.        
These examples show that the term “transmission” is to be understood here in the general meaning, namely as a kinematic device which is used for coupling and converting movements. The transmission links are the coupling elements of a transmission in this meaning. In the known housing-coupled drives, the housing coupling mechanism provides a precise coupling between the lancing element and the housing, at least at the reversal point of the lancing movement, in such a manner that the reversal point of the lancing movement has a defined specified distance to the housing bearing (which is fixed on the housing at least at the reversal point of the lancing movement).